Biorefineries producing commodities from renewable resources offer an alternative to oil refineries based on dwindling supplies of petroleum and permit a move towards improved energy security. Lignocellulosic residues from forestry and agriculture are attractive as feedstocks, since they are abundant, relatively inexpensive, and are not used for food. Lignocellulose consists mainly of lignin and two classes of polysaccharides, cellulose and hemicellulose. The polysaccharides can be hydrolyzed to sugars and converted to various fermentation products, such as bioalcohols, in processes based on biocatalysts, such as the industrially important baker's yeast (Saccharomyces cerevisiae).
The hydrolysis of cellulose is typically preceded by a pretreatment, in which the hemicellulose is degraded and the cellulose is made increasingly accessible to cellulolytic enzymes. However, the pretreatment process typically generates fermentation inhibitors, such as phenolic compounds, aliphatic acids, and furan aldehydes, which have a negative effect on the efficiency of the fermentation process. Furthermore, it may be desirable to recirculate process water to achieve a cost-efficient and environmentally sound process. Such recycling of process may lead to accumulation of inhibitors that will contribute to the problems of poor fermentability.